'Satan Nostradamus' not guilty of killing mother

A delusional man, who fatally stabbed his mother and said his name was Satan Nostradamus, has been found not guilty of her murder because of mental illness.

Benjamin James Watson's delusions included a firm belief that Helen Fay Watson was not his real mother but was "a keep", which he said meant his parents "pay her to look after me".

In the past, Ms Watson expressed fears about her son, saying he had threatened her and became obsessed with knives.

At times when he was significantly paranoid, she had to lock him out of the house and also stayed elsewhere.

The 31-year-old was charged with murdering Ms Watson at Lake Bathurst, outside Goulburn, in March last year.

In the NSW Supreme Court on Friday, Justice Monika Schmidt concluded Watson not guilty on the grounds of mental illness.

"The accused suffers from a persistent, treatment-resistant form of paranoid schizophrenia," she said.

"As a result, he has long suffered from paranoia and persistent hallucinations and delusional beliefs, including long-held beliefs about his relationship with his mother and the serious harm she has done him."

The judge said Watson apparently was not frank with his treating psychiatrist about his ongoing symptoms or the side effects of his medication.

Side effects

He sought to have his medication reduced in order to alleviate the side effects.

"In March 2010, the accused was on a seemingly low dose of medication, which was then reduced even further even though he was in fact acutely ill," Justice Schmidt said.

"The further reduction of his medication appears to have exacerbated the side effects which he was experiencing."

The judge said the end result was that he killed his mother at a time "he was not able to understand that what he was doing, when he caused her death, was wrong".

Ms Watson died from multiple stab and cut wounds.

When police arrived he told them he had another name, Satan Nostradamus, which his real mother had given him.

Watson, who had spent time in psychiatric wards, had a long history of mental illness when he heard voices, hallucinated and had persecutory beliefs.

Justice Schmidt ordered Watson be detained at a jail hospital until, and if, the Mental Health Review Tribunal deems him not to be a danger to the community or himself.